Conventionally, there have been proposed image processing methods of transmitting an image by dynamically changing a compressing method depending on image information or a condition of communication paths. The known methods include, for example, a method described in Japanese Unexamined Patent Publication (Kokai) No. H10-145796, pages 9 and 10 (first method). The entire disclosure of Japanese Unexamined Patent Publication (Kokai) No. H10-145796 is incorporated herein by reference in its entirety.
First, the first method will be explained. FIG. 11 shows a coding apparatus 101 employing the first method. The coding apparatus 101 includes switches SW1 and SW2 of switching compressing methods, a predictive coder 102, a variable length coder 103, and an MPEG coder 104.
According to this method, a movable region is first detected within an image read from a memory. Next, performing histogram processing to the detected region, it is determined whether or not the image is similar to a natural image, and based on the determination result, the switches SW1 and SW2 are then switched. As a result of this, the dynamic image can be MPEG-coded by the MPEG coder 104, while the other types of images may be compressed by the predictive coder 102 and the variable length coder 103.
Japanese Unexamined Patent Publication (Kokai) No. 2001-36655 describes the invention of calculating data transmission speed on a network when image data is transmitted via the network to downsize the image data to be transmitted based on the calculated data transmission speed (second method). The entire disclosure of Japanese Unexamined Patent Publication (Kokai) No. 2001-36655 is incorporated herein by reference in its entirety. According to this invention, it is described the method of resizing the image data or varying a compression ratio so that the transmission time may be kept constant by reducing a data amount.
In the case of the first method, since histogram is used to determine whether or not the detected moving region is similar to the natural image, it takes a certain amount of time to determine the natural image region, and in addition to that, the determination is frequently mistaken, resulting in difficulty in achieving high-speed. Meanwhile, in the case of the second method, since the image compression ratio is changed according to the transmission speed, high-speed transmission has been able to be achieved, but the method has been disadvantageous since image distortion has often occurred due to the change in the compression ratio regardless of image characteristics.
As a result, there still remain problems that to achieve the high-speed transmission is difficult, and the image distortion is likely to occur even if the high speed transmission is established.